It is known that satellite radio telephones have been developed and deployed throughout the world, especially where topographical conditions preclude use of conventional mobile radio telephones or fixed wire telephones, for example in rugged terrain areas or sparsely populated areas. These systems typically are understood to provide both voice and data communications so that they may include terminals such as PCS terminals.
Prior art satellite radio telephone systems may be broadly classified into two types: mobile satellite radio telephone systems and fixed satellite radio telephone systems. In each of these systems one or more satellites are used to communicate with radio telephones, the satellites being either orbiting satellites or geostationary satellites. Typically, a mobile satellite radio telephone system is designed to communicate with a plurality of mobile radio telephones of similar size as conventional cellular radio telephones, whereas a fixed satellite radio telephone system is designed to communicate with a plurality of fixed or non-mobile radio telephones using permanent or semi-permanent fixed antennas which may be mounted on buildings or homes.
Consequently, it is found the capacity of fixed satellite radio telephone systems is much larger than that associated with mobile satellite radio telephone systems where a significantly lower number of radio telephones are served than in a fixed satellite system.
Generally, the per-satellite capacity of a satellite radio telephone is limited by the amount of satellite power that is expended per communication circuit in order to establish and maintain communications with a radio telephone. In addition, limiting factors such as available frequency spectrum and the typically poor frequency reuse of satellite radio telephone systems impact the per-satellite capacity of these phones.
Consequently, mobile satellite radio telephone systems have been found to generally possess much lower capacity than fixed satellite radio telephone systems. Both regional and global mobile satellite systems are found to be quite limited in capacity, the regional mobile satellite systems involving geostationary satellites having, for example, a capacity per satellite of about 10,000 simultaneous radio telephone communications, whereas global mobile satellite systems involving both medium earth orbiting satellites, or MEOs, or low earth orbiting satellites, or LEOs, generally have even lower capacity per satellite ranging into the 3,000-4,000 simultaneous radio telephone communications.
It is understood that the per-satellite capacity of mobile satellite radio telephone systems is the amount of power that is expended per communication by the satellite payload in order to establish and maintain communications with the small hand held mobile phones. The practical limitations involved in forming a very large number of spot beams from the satellite often limits frequency reuse for mobile satellite radio telephone systems resulting in generally low capacities of said systems.
Prior art mobile satellite systems employing radio telephones or MSS are known in the art; for example, in U.S. Pat. No. 5,303,286 to Globalstar® a satellite communication system having at least one, but usually a plurality, of orbiting satellites over a terrestrial satellite service area, a satellite control center and a plurality of terrestrial communication links wherein call setup is controlled by processors and databases onboard the orbiting satellites and where only after the satellite link for the communication channels is completed, does control and switching rely on ground based systems such that the orbiting satellites are integrated into a ground based telephone network and tariff structure.
In U.S. Pat. No. 5,715,297 to Globalstar® there is disclosed a radio communication system capable of servicing a roaming user or the like outside the range of terrestrial relay stations which includes a packet switched network and database of roaming users and a satellite communications system having at least one, but usually a plurality, of orbiting satellites over a terrestrial satellite service area, a satellite control center and a plurality of terrestrial communication links, wherein cell setup is controlled by processors and databases onboard the orbiting satellites and wherein only after the satellite link for the communication channels is completed, does control and switching rely on ground based equipment such that the orbiting satellites are integrated to a ground based telephone network and tariff structures. Similar systems and improvements thereto, as found in the U.S. Pat. Nos. 5,303,286 and 5,715,297, include those defined in U.S. Pat. No. 5,903,837 and U.S. Pat. No. 6,072,768.
Various other systems have been proposed as depicted in the FCC filing for “Authority to Launch and Operate a Satellite System to Provide Mobile Satellite Services in the 2 GHz Bands” dated Nov. 3, 2000, relating to the Globalstar® system, which is hereby incorporated by reference; the FCC filing in the matter of Mobile Satellite Ventures Subsidiary, LLC for “Minor Amendment of Application to Launch and Operate a Replacement L Band Mobile Service Satellite at 101° West” dated Nov. 18, 2003; and the FCC filing by Thoraya which depicts a one GEO satellite system to provide a satellite telephone service; and the Iridium system produced by Motorola generally described in U.S. Pat. Nos. 5,918,176 and 5,490,087, in addition to the above recited Globalstar® systems.
Prior art methods to increase the relatively limited capacity of mobile satellite radio telephone systems experiencing capacity bottlenecks or hot spots which are developed in congested areas of the mobile satellite radio telephone system where the mobile satellite radio telephone system (MSS) does not have enough capacity to accommodate all users, so that it is difficult to increase the capacity of the MSS in these congested areas.
Consequently, methods and systems to increase the capacity of MSS include allowing an MSS to use some of the capacity of a fixed satellite system in areas of congestion, such as defined in U.S. Pat. No. 6,052,586.
In addition to improving cellular satellite communication systems and methods to provide wireless communications employing at least one space based component such as one or more satellites that are configured to wirelessly communicate with a plurality of radio telephones or other types of cellular terminals, hybrids of satellite and terrestrial systems have been developed and used wherein terrestrial networks enhance cellular satellite communications system availability, efficiency and/or economic viability by terrestrially reusing at least some of the frequency bands allocated to cellular satellite communication systems. Difficulty is experienced for cellular satellite communication systems to reliably serve densely populated areas where the satellite signal may be blocked by high rise structures or may not penetrate into buildings. In such cases, the satellite spectrum may be underutilized or unutilized in such areas. It is found that the use of terrestrial retransmission can reduce or eliminate this problem. Thus, the capacity of the overall system can be increased significantly by the introduction of terrestrial retransmission since terrestrial frequency reuse can be much denser than that of a satellite-only system. It is further found that capacity can be enhanced where it may be mostly needed, for example, densely populated urban/industrial/commercial areas so that the overall system can become much more economically viable as it is seen to be able to serve a much larger subscriber base.
One example in the prior art of terrestrial reuse of satellite frequencies is described in U.S. Pat. No. 5,937,332 entitled “Satellite Telecommunications Repeaters and Retransmission Methods”. Generally described therein, satellite communication repeaters are provided which receive, amplify and locally retransmit the downlink signal received from a satellite, thereby increasing the effect of downlink margin in the vicinity of the satellite telecommunications repeaters and allowing an increase in the penetration of uplink and downlink signals into buildings, foliage, transportation vehicles and other objects which can reduce link and margin.
Methods and systems in the prior art allow a satellite radio telephone frequency to be reused terrestrially within the same satellite cell while allowing intrasystem interference to be reduced. These systems include a space based component such as a satellite that is configured to receive wireless communications from a first radio telephone in a satellite footprint comprising one or more cells over a satellite radio telephone frequency band. There is also provided an ancillary terrestrial network comprising one or more ancillary terrestrial components configured to receive wireless communications from a second radio telephone in the satellite footprint over the satellite radio telephone frequency band. The wireless communications from the second radio telephone are also received by the space based component in the satellite footprint over the satellite radio telephone frequency band as interference, along with the wireless communications that are received from the first radio telephone in the satellite footprint over the satellite radio telephone frequency band. In such cases, an interference reducer is employed that is responsive to the space based component and to the ancillary terrestrial network and that is configured to reduce the interference from the wireless communications that are received by the space based component from the first radio telephone in the satellite footprint over the satellite radio telephone frequency band using the wireless communications that are received by the ancillary terrestrial network from the second radio telephone in the satellite footprint over the satellite radio telephone frequency band.
Other wireless communications systems including a satellite gateway coupled to a communications network and operative to communicate with a communications satellite include a terrestrial terminal interface subsystem operative to communicate with a satellite gateway via the communications satellite using a first radio interface and to communicate with wireless terminals over a geographic area using a second radio interface, for example, as defined in U.S. Pat. No. 6,856,787.
Other cellular systems comprise a space based system including a first set of cells and a ground based system including a second set of cells. In such systems the space and ground systems can optionally function substantially autonomously with each using spectrum from at least one predetermined frequency band, for example, as described in U.S. Pat. No. 6,859,652.
All of the above recited systems are found to be expensive to fabricate, install and maintain, especially those employing satellite communications. Two such systems, Globalstar® and Iridium, each cost in the billions of dollars to develop, fabricate and launch and potentially hundreds of millions of dollars to maintain over their lifetimes. It is thus seen to be imperative to sustain the systems and make them commercially viable that every avenue be explored to generate revenue, including ATC systems and preferably methods and systems be developed and employed to enhance, improve and/or optimize the systems.
Consequently, prior art systems and methods to address intrasystem interference and reduction of same have been developed and employed.
In U.S. Pat. No. 5,875,180 a method is disclosed for operating a first satellite communication system of a type that operates co-frequency with at least one second transmission system such as a second satellite communication system. The method includes steps executed during the operation of the first satellite communication system, of measuring at least a plurality of locations within a coverage area of the first system an amount of interference resulting at least in part from the at least one second transmission system, the amount of interference being measured over a band of frequencies allocated to the first system; transmitting an indication of the measured interference from each location to a central site; and in accordance with the transmitted indications, assigning at least one user terminal to a sub-band of frequencies within the band of frequencies so as to reduce an amount of interference experienced by the user terminal.
In U.S. Pat. No. 5,905,943 there is disclosed a method for defining a radio frequency map to be used to isolate negative effects of undesirable radio frequency emitters on radio device communications handheld and stationary. The method includes the steps of measuring C-band power corresponding to an L-band beam as a part of an L-band footprint of a communication satellite, calculating various identifiable interference errors associated with the signal transmission path, and subtracting the interference errors from the original C-band power measurement resulting in a power value corresponding to undesirable radio frequency emitter interference at the location of the L-band beam. The resulting radio frequency map can then be used to reallocate frequency channels of operation used by radio devices, mobile phones for example, resulting in power savings in the radio device while maintaining a suitable signal to noise ratio.
In U.S. Pat. No. 6,879,829 there is disclosed a satellite communications system includes a satellite that is configured to wirelessly communicate with radioterminals in a satellite coverage area over a satellite frequency band, and an ancillary terrestrial component that is configured to wirelessly communicate with radioterminals in the satellite coverage area over at least some of the satellite frequency band, to thereby terrestrially reuse at least some of the satellite frequency band. Wireless communications with a radioterminal are handed over from the ancillary terrestrial component to the satellite if the radioterminal transmit power exceeds a threshold, and a received satellite signal quality exceeds a threshold, even though the radioterminal is able to wirelessly communicate with the ancillary terrestrial component. Downlink wireless radiation that is received at the radioterminal from a satellite may be monitored to determine potential interference created by the uplink radiation of the radioterminal due to the terrestrial reuse of at least some of the satellite frequency band.